[en] Based on a 5-year study of the International Institute for Applied Systems Analysis, Laxenburg, Austria, this paper identifies the factual basis of today's energy situation, stressing the need for and difficulties in long-term supranational energy supply strategies. The bases are two scenarios - defined by close to observed trends of population and economic growth - that indicate a conceivable energy demand range until 2030. These scenarios are quantified for seven comprehensive world regions by way of a highly iterative model set designed at IIASA to study long-term, dynamic, and regional/global aspects of large-scale energy systems. The results illustrate the need for the world to use all available, and high-cost, energy sources. Nuclear and solar technologies replacing fossil resources will fully have to come to bear after 2030